Use as corrosion inhibitors:acridine phosphoric compounds

ABSTRACT

A process of inhibiting corrosion of ferrous metals wherein the metal is contacted with a corrosion inhibiting amount of a full nitrogen heterocyclic phosphoric compound having the phosphorous atom of the phosphoric group bonded directly to a carbon atom of said nitrogen heterocyclic group and wherein said phosphoric group is para to the nitrogen atom on said nitrogen heterocyclic group. Preferred embodiments of the corrosion inhibitor are diethyl acridine-9-phosphonate and acridine-9-phosphoric acid.

i United States Patent Redmore Apr. 29, 1975 USE As CORROSION 13.591.330 7/1971 Redmore 21/25 A INHIBITORS=ACRID1NE PHOSPHORIC3,664,807 5/1972 Redmore 21/25 A COMPOUNDS 3,673,196 6/1972 Redmorc260/286 A X 3,694.144 9/1972 Redmore 21/27 A [75] inventor: DerekRedmore, Ballwin, M 3,711,404 1/1973 Redmorc 1 252/8.55 E 3,720,4983/1973 Rcdmore 21/2.5 A 1 Asslgneer Petrol! cflrporamn, wllmmgtonv3,775,057 11 /1973 Redmore 21/25 A 1391- 3,809,694 5 1974 Redmore260/286 A [22] Filed: g 10, 1973 3,810,907 5/1974 Redmorc 260/297 P pp387,293 Primary ExaminerBarry S. Richman Related Application Damgiro/My, Agent, or Firm-Sidney B. Ring; Hyman F. [60]Continuation-impart of Scr. NO. 173,296, Aug. 19, ass

1971, Pat. No. 3,775,057, which is a division of Scr. NO. 801,856, Feb.24, 1969, Pat. NO. 3,673,196. [57] ABSTRACT A process of inhibitingcorrosion of ferrous metals [52] Cl 21/25 A; 21/27 A 252/8'55 E; whereinthe metal is contacted. with a corrosion inhib- 252/146; 252/148;252/151; 25 A iting amount ofa full nitrogen lheterocyclic phosphoric[51] 9' 11/163 C23f H/OO; C23f 11/04 compound having the phosphorousatom of the phos- [58] Field of Search 252/389 A, 8.55 Z, 146, phoricgroup bonded direetly to a Carbon atom of said 252/148, 151; 106/14;260/283 P, 297 P; nitrogen heterocyclic group and wherein said phos-2l/2'5 A phoric group is para to the nitrogen atom on said nitrogenheterocyclic group. Preferred embodiments of [56] References cued thecorrosion inhibitor are diethyl acridine-9- UNITED STATES PATENTSphosphonate and acridine-9-phosphoric acid. 2,957,931 10/1960 Hamiltonet a1 260/283 P UX 3,216,894 1 1/1965 Lorenz 6t 11. 260/283 P 3 DrawmgsUSE AS CORROSION INHIBITORSzACRIDINE PHOSPHORIC COMPOUNDSContinuation-impart of Ser, No. 173,296 filed Aug. 19, 1971 now US. Pat.No. 3,775,057, which is a division of Ser. No. 801,856 filed Feb. 24,1969, now US. Pat. No. 3,673,196.

This invention relates to nitrogen-heterocyclic phosphonates. Moreparticularly this invention relates to nitrogen-heterocyclicphosphonates wherein the phosphonate group is ortho or para to theheterocyclic nitrogen group. Still more particularly, this inventionrelates to compounds characterized by the following groups:

(ortho substituted) (para substituted) This invention also relates touses for these compounds for example as biocides, such as bacteriocides,herbicides, corrosion inhibitors, chelating agents, etc.

In my application Ser. No. 733,328 filed May 31, 1968 and now abandoned,there are described and claimed processes for preparing dihydro nitrogenheterocyclic phosphonates and the resulting phosphonates which aresubstituted ortho and/0r para to the heterocyclic nitrogen atom, etc.For example, the invention of Ser. No. 733,328 may be illustrated by thefollowing equations:

+ R OH MX R,, R2, R R R R may be hydrogen or a substituted group, forexample, alkyl, cycloalkyl, aryl, alkaryl. aralkyl, etc.

R, is an ester moiety for example alkyl. aryl, cycloalkyl, aralkyl,alkaryl, etc. oxyalkylated groups, etc.

The groups of R, to R may also be further substituted provided thesubstituted groups do not interfere with the reaction.

X is any suitable anion, for example, halogen, e.g. chlorine, bromine,iodine, etc., SO,,R, SO R where R is alkyl, etc., such as -SO,Me, SO,Et,

etc.

The present invention relates to a process of preparaing analogousnitrogen heterocyclic phosphonates as contrasted to thedihydro-heterocyclic phosphonates of Ser. No. 733,328 (i.e. fullheterocyclic as contrasted to dihydro-heterocyclic).

The present invention may be illustrated by the following equations:

(where R is hydrogen) where R, is a hydrocarbon group such as alkyl,cycloalkyl, aryl, aralkyl, alkaryl, etc., R R R R R is hydrogen or asubstituted group, for example, alkyl, cycloalkyl, aryl, alkaryl,aralkyl, etc.

R, is an ester moiety for example alkyl, aryl, cycloalkyl, aralkyl,alkaryl, etc. oxyalkylated groups, et.

The groups of R, to R, may also be further substituted provided thesubstituted groups do not interfere with the reaction.

X is any suitable anion, for example, halogen, e.g. chlorine, bromine,iodine, etc., 50 R, -SO,,R, where R is alkyl, such as SO,Me, SO.,Et,

etc.

It is to be noted that in the invention described in Ser. No. 733,328the R, group remains affixed to the heterocyclic nitrogen throughout thereaction and in the final product, thus yielding a dihydro derivative ofa heterocyclic compound; whereas in the present invention the nitrogenbonded OR, group is removed as an alcohol moiety during the reaction toyield the heterocyclic compound itself. 7 a r In preparing the compoundsof this invention it is convenient to start with nitrogen-heterocycliccompound, oxidize it to the N-oxide, react this with an alkyl ester ofan inorganic acid such as alkyl halide, alkyl sulfate, etc. to form theOR, group, and to then react the salt of a phosphite ester to yield theheterocyclic phosphonate as illustrated by the following series ofreactions:

R I R i i (OR) (where R is hydrogen 0 ll H011 l and/or P(0 7) Anynitrogen heterocyclic having an available ortho and/or para positioncapable of being activated by quaternary formation of the nitrogen groupwith an -OR group so as to promote reaction with salts of phosphiteesters can be employed. This includes heterocyclics having one or morerings, where at least one ring has a nitrogen heterocyclic group and theother rings are carbocyclic or heterocyclic, i.e., they may containoxygen or other non-carbon elements in the ring, etc. for example,

co 011:1 ms

The above ring systems may also be substituted. The

etc.

phite salt so that phosphonate substitution may occur in more than onering.

X is any suitable anion, for example, halogen, e.g. chlorine, bromine,iodine, etc., SO R, SO R where R is alkyl such as SO Me, SO Et,

I so

metal salt in which the metal is directly bonded to phosadjacent ringsmay also contain heterocyclic groups for 45 phorous. In order to preventundesirable side reactions example oxygen, nitrogen, etc., and/or maycontain rings having less than six molecules in the ring for example a 5member ring.

In certain instances more than one nitrogen heterocyclic ring may becapable of reacting with the phosthe phosphorous acid is used in theform of a derivative, preferably as a diester.

Where the phosphite ester contains more than one phosphite unit, aplurality of heterocyclic units may be 50 joined thereto, for example 78 1 11 R P-(oM o OH Ro- N/MW M G; i 1 O 1 ROl- (0A) orLoja and/or- Roi(0A) -/loi on. :TN N \4 2 u :1 \N \N i? 9 and/or 'ROI (0A) Cliff Ingeneral, the reaction is carried out in an inert solvent which is waterfree at a temperature and time sufficient to promote the desiredreaction. Ether solvents such as diethyl ether, dioxane andtetrahydrofuran are useful as well as aromatic hydrocarbon solvent likebenzene, toluene, etc. Particularly useful are dipolar aprotic solventssuch as dimethyl sulfoxide, dimethyl formamide N-methyl pyrrolidone.Combinations of these various types of solvents can also beadvantageously used. Temperature and time are interrelated. Thus, atemperature of from 30 to the decomposition temperature of reactants andproducts can be employed, the upper limit of temperature being generallyabout 150C., for a time of from 0.5-l0 hours but preferably -l-3 hours.The inorganic salt is separated from the organic layer by filtration orby water extraction and the phosphonate derivative is separated from theorganic layer. In addition the reaction is best carried out on an inertatmosphere such as nitrogen, argon, etc. In this way the attack ofoxygen on phosphite salts and on the products is prevented.

The following eamples are presented by way of illustration and not oflimitation.

EXAMPLE 1 Diethyl Pyridine 2-phosphonate To pyridine N-oxide (19g; 0.2mole) was added dimethyl sulfate (25.2g; 0.2 mole) during 30 minutes.The reaction was completed by heating at 100C. for 2 hours yieldingN-methoxy pyridinium methosulfate. Diethyl sodio phosphonate wasprepared by dissolving sodium (4.6g; 0.2 mole) in a solution of diethylphosphite (27.6g; 0.2 mole) in dioxane (100 ml) in an argon atmosphere.The N-methoxy pyridinium quaternary was suspended in toluene by stirringwhile the diethyl sodio phosphonate solution was added. The reactionflask was cooled to maintain the temperature at 35C. After stirring for1% hours water (100 ml) was added and the organic product isolated bychloroform extraction. Evaporation of the chloroform extract anddistillation yielded diethyl pyridine-2-phosphonate with a small amountof diethyl pyridine 4-phosphonate. Yield 14g (33%) bp 8C./l.5 mm. Thepresence of the two isomers was established by infrared absorption;2-isomer 13.3 p. (strong, 4 adjacent hydrogen) and 4isomer, 12.3 1.(weak, 2 adjacent hydrogen).

EXAMPLE 2 Diethyl 4-methyl Pyridine-Z-Phosphonate N-methoxy-4-methylpyridinium methosulfate was prepared from 4-picoline-N-oxide (54.4g; 0.5mole) and dimethyl sulfate (63g; 0.5 mole) and suspended by stirringwith toluene (250 ml). To this suspension was added diethyl sodiophosphonate in dioxane ml) prepared from diethyl phosphite (69g; 0.5mole) and sodium (11.5g; 0.5 mole). This addition was carried out in 40minutes during which time the temperature was controlled at 45C. bycooling. After stirring for one hour water was added to the reaction andthe product isolated by chloroform extraction. Evaporation anddistillation yielded diethyl 4-methyl pyridine-2- phosphonate 17g; bpl09l 120.05 mm. The infrared spectrum shows absorption at 7.97 .:.(P=O),9.8g. and 10.4 p.(PO-C).

EXAMPLE 3 Diethyl Quinoline-Z-Phosphonate and -4-PhosphonateN-methoxyquinolinium methosulfate was prepared from quinoline N-oxide(50g; 0.344 mole) and dimethyl sulfate (43.5g; 0.344 mole). To thisquaternary was added diethyl sodiophosphonate from diethyl phosphite(47.5g; 0.344 mole) and sodium (7.9g; 0.344 mole) in dioxane (100 ml.).The reaction was completed by heating at l00-l 10C. for two hours. Waterwas added to the reaction, after cooling, and the product was isolatedby benzene extraction. Evaporation of the solvent and heating undervacuum at l40C./2 mm gave a residue which was a mixture of diethylquinoline Z-phosphonate and 4-phosphonate. Analysis found N 5.4%calculated N. 5.28%.

EXAMPLE 4 Diethyl lsoquinoline -l- Phosphonate N-methoxy isoquinoliniummethosulfate was converted by reaction with diethyl sodio phosphonate indioxane into diethyl isoquinoline-l-phosphonate in yield using theprocedure of Example 3. The product was purified by distillation bp llC./O.l5

EXAMPLE 5 Diethyl 4-Cyanopyridine -2- Phosphonate EXAMPLE 6 4-MethylPyridine -2- Phosphonic Acid Diethyl 4-methyl pyridine -2-phosphonate (1lg.) (The product from Example 2) was heated for six hours with 18%hydrochloric acid (120 ml) at 100. The acid was removed under vacuum toleave a gum which was dissolved in ethyl alcohol. Addition of etheryielded white crystals which after drying gave pure 4-methyl pyridine-2- phosphonic acid (7.2g; 86% )mp 2726C.

Analysis Calculated: C Found: C

EXAMPLE 7 Quinoline 2- and 4- Phosphonic Acids The product of Example 3(7.7g) was heated under reflux for 3 /2 hours with 18% hydrochloric acid(60 ml.). Using the isolation procedure of Example 6 a crude quinolinephosphonic acid 5g. (82%) was iso lated. Crystallization from aceticacid gave pure quinoline -2- phosphonic acid mp 200C.

Analysis Calculated: N, 6.7071; P. l4.837(. Found: N, 6.33%; P, l4.7l/?.

As is quite evident, other nitrogen heterocyclics and phosphites areuseful in my invention. It is, therefore, not only impossible to attempta comprehensive catalogue of such compounds, but to attempt to describethe invention in its broader aspects in terms of specific heterocyclicsand phosphites reacted would be too voluminous and unnecessary since oneskilled in the art could by following the description of the inventionherein select a useful reactant. This invention lies in the reaction ofsuitable heterocy clics and phosphites and their individual compositionsare important only in the sense that they react to form useful products.To precisely define each specific useful heterocyclic in light of thepresent disclosure would merely call for chemical knowledge within theskill of the art in a manner analogous to a mechanical engineer whoprescribes in the construction of a machine the proper materials and theproper dimensions thereof. From the description in this specificationand with the: knowledge of a chemist, one will know or deduce withconfidence the applicability of specific heterocyclics suitable for thisinvention. In analogy to the case of a machine, wherein the use ofcertain materials of construction or dimensions of parts would lead tono practical useful result, various materials will be rejected asinapplicable where others would be operative. I can obviously assumethat no one will wish to use a useless heterocyclic nor will be misledbecause it is possible to misapply the teachings of the presentdisclosure to do so. Thus, any heterocyclic that can react as statedherein can be employed. Similarly any nitrogen heterocyclic phosphonatewhich is within the scope of this invention and effective as a corrosioninhibitor (as hereinafter stated) is within the scope of this invention.

USE AS CORROSION INHIBITORS This phase of this invention relates to theuse of the present compounds in inhibiting the corrosion of metals, mostparticularly iron, steel and ferrous alloys. These compounds can be usedin a wide variety of applications and systems where iron, steel andferrous alloys are affected by corrosion. They may be employed forinhibiting corrosion in processes which require this protective orpassivating coating as by dissolution in the medium which comes incontact with the metal. They can be used in preventing atmosphericcorrosion, underwater corrosion, corrosion in steam and hot watersystems, corrosion in chemical industries, underground corrosion, etc.

The corrosion inhibitors contemplated herein find special utility in theprevention of corrosion of pipe or equipment which is in contact with acorrosive oilcontaining medium, as, for example, in oil wells producingcorrosive oil or oil-brine mixtures, in refineries, and the like. Theseinhibitors may, however, be used in other systems or applications. Theyappear to possess properties which impart to metals resistance to attackby a variety of corrosive agents, such as brines, weak inorganic acids,organic acids, CO H 8, etc.

The method of carrying out this process is relatively simple inprinciple. The corrosion preventive reagent is dissolved in the liquidcorrosive medium in small amounts and is thus kept in contact with themetal surface to be protected. Alternatively, the corrosion inhibitormay be applied first to the metal surface, either as is, or as asolution in some carrier liquid or paste. Continuous application, as inhe corrosive solution, is the preferred method, however.

The present process finds particular utility in the protection of metalequipment of oil and gas wells, especially those containing or producingan acidic constituent such as H 5, CO organic acids and the like. For

the protection of such wells, the reagent, either undiluted or dissolvedin a suitable solvent, is fed down the annulus of the well between thecasing and the producing tubing where it becomes comingled with thefluid in the well and is pumped or flowed from the well with thesefluids, thus contacting the inner wall of the casing, the outer and theinner wall of tubing, and the inner surface of all wellhead fittings,connections and flow lines handling the corrosive fluid.

Where the inhibitor composition is a liquid, it is conventionally fedinto the well annulus by means of a motor driven chemical injector pump,or it may be dumped periodically (e.g., once every day or two) into theannulus by means of a so-called bole weevil" device orsimilar'arrangement. Where the inhibitor is a solid, it may be droppedinto the well as a solid lump or stock, it may be blown in as a powderwith gas, or it may be washed in with a small stream of the well fluidsor other liquid. Where there is gas pressure on the casing, it isnecessary, of course, to employ any of these treating methods through apressure equalizing chamber equipped to allow introduction of reagentinto the chamber equalization of pressure between chamber and casing,and travel of reagent from chamber to well casing.

Occasionally, oil and gas wells are completed in such a manner thatthere is no opening between the annulus and the bottom of the tubing orpup. This results, for example, when the tubing is surrounded at somepoint by a packing held by the casing or earth formation below by thecasing. In such wells the reagent may be introduced into the tubingthrough a pressure equalizing vessel, after stopping the flow of fluids.After being so treated the well should be left closed in for a period oftime sufficient to permit the reagent to drop to the bottom of the well.

For injection into the well annulus, the corrosion inhibitor is usuallyemployed as a solution in a suitable solvent. The selection of solventwill depend much upon the exact reagent being used and its solubilitycharacteristics.

For treating wells with packed-off tubing, the use of solid sticks orplugs of inhibitor is especially convenientt These may be prepared byblending the inhibitor with a mineral wax, asphalt or resin in aproportion sufficient to give a moderately hard and high-melting solidwhich can be handled and fed into the well conveniently.

The protective action of the herein described reagents appears to bemaintained for an appreciable time after treatment ceases, buteventually is lost unless another application is made.

For example, for the protection of gas wells and gascondensate wells,the amount of corrosion inhibitor I used might range between about A to3 lbs. more per million cubic feet of gas produced, depending upon theamounts and composition of corrosive agents in the gas and the amount ofliquid hydrocarbon and water produced. However, in no case does theamount of inhibitor required appear to be stoichiometrically related tothe amount of acids produced by a well, since protection is obtainedwith much less corrosion inhibitor than usually would be required forneutralization of the acids produced.

These compositions are particularly effective in the prevention ofcorrosion in systems containing a corrosive aqueous medium, and mostparticularly in systems containing brines.

These compounds can also be used in the prevention of corrosion in thesecondary recovery of petroleum by water flooding and in the disposal ofwaste water and brine from oil and gas wells. Still more particularly,they can be used in a process of preventing corrosion in water floodingand in the disposal of waste water and brine from oil and gas wellswhich is characterized by injecting into an underground formation anaqueous solution containing minor amounts of the compositions of thisinvention, in sufficient amounts to prevent the corrosion of metalsemployed in such operation.

When an oil well ceases to flow by the natural pressure in the formationand/or substantial quantities of oil can no longer be obtained by theusual pumping methods, various processes are sometimes used for thetreatment of the oil-bearing formation in order to increase the flow ofoil. These processes are usually described as secondary recoveryprocesses. One such process which is used quite frequently is the waterflooding process wherein water is pumped under pressure into what iscalled an injection well and oil, along with quantities of water, thathave been displaced from the formation, are pumped out of an adjacentwell usually referred to as a producing well. The oil which is pumpedfrom the producing well is then separated from the water that has beenpumped from the producing well and the water is pumped to a storagereservoir from which it can again be pumped into the injection well.Supplementary water from other sources may also be used in conjunctionwith the produced water. When the storage reservoir is open to theatmosphere and the oil is subject to aeration this type of waterflooding system is referred to herein as an open water flooding system.If the water is recirculated in a closed system without substantialaeration, the secondary recovery method is referred to herein as aclosed water flooding system.

Because of the corrosive nature of oil field brines, to economicallyproduce oil by water flooding, it is necessary to prevent or reducecorrosion since corrosion increases the cost thereof by making itnecessary to repair and replace such equipment at frequent intervals.These compositions can be employed in preventing corrosion in systemscontaining a corrosive aqueous media, and most particularly in systemscontaining brine, which is characterized by employing the phosphonatecompounds described herein. For example, they can be employed in animproved process of protecting from corrosion metallic equipmentemployed in secondary oil recovery by water flooding such as injectionwells, transmission lines, filters, meters, storage tanks, and othermetallic implements employed therein and particularly those containingiron, steel, and ferrous alloys, such process being characterized byemploying in water flood operation an aqueous solution of thecompositions of this invention.

In many oil fields large volumes of water are produced and must bedisposed of where water flooding operations are not in use or wherewater flooding operations cannot handle the amount of produced water.Most States have laws restricting pollution of streams and land withproduced waters, and oil producers must then find some method ofdisposing of the waste produced salt water. In many instances therefore,the salt water is disposed by injecting the water into permeable lowpressure strata below the fresh water level. The formation into whichthe water is injected is not the oil producing formation and this typeof disposal is defined as salt water disposal or waste water disposal.The problems of corrosion of equipment are analogous to thoseencountered in the secondary recovery operation by flooding. Thecompositions of this invention can also be used in such water disposalwells thus providing a simple and economical method of solving thecorrosion problems encountered in disposing of unwanted water.

Water flood and waste disposal operations are too well known to requirefurther elaboration. In essence, the flooding operation is effected inthe conventional manner except that the flooding medium contains a minoramount of these compounds, sufficient to prevent corrosion.

While the flooding medium employed in accordance with the presentinvention contains water or oil field brine and the compounds of thisinvention, the medium may also contain other materials. For example, theflooding medium may also contain other agents such as surface activeagents or detergents which aid in wetting throughout the system and alsopromote the desorption of residual oil from the formation, sequesteringagents which prevent the deposition of calcium and/or magnesiumcompounds in the interstices of the formation, bacteriocides whichprevent the formation from becoming plugged through bacterial growth,tracers, etc. Similarly, they may be employed in conjunction with any ofthe operating techniques commonly employed in water flooding, peripheralflooding, etc. and in conjunction with other secondary recovery methods.

The concentration of the corrosion inhibitors of this invention willvary widely depending on the particular compound, the particular system,etc. Concentrations of at least about 0.25 ppm, such as about 0.75 to7,500 ppm for example about 1 to 5,000 ppm, advantageously about to1,000 ppm, but preferably about -250 ppm may be employed. Larger amountscan also be employed such as l.55.0% although there is generally nocommercial advantage in so doing.

For example, since the success of a water flooding operation manifestlydepends upon its total cost being less than the value of the additionaloil recovered from the oil reservoir, it is quite important to use aslittle as possible of these compounds consistent with optimum corrosioninhibition.

Since these compounds are themselves inexpensive and are used in lowconcentrations, they enhance the success of a flood operation bylowering the cost thereof.

By varying the constituents of the composition, the compounds of thisinvention can be made more oil or more water soluble, depending onwhether the composition is to be employed in oil or water systems.

These compounds can also be employed in conjunction with other corrosioninhibitors, for example, of the filmforming type. Non-limiting examplesinclude the acylated polyamines such as described in U.S. Pat. Nos. Re.23,227, 2,466,517, 2,468,163, 2,598,213 and 2,640,029. These acylatedpolyamines may be described as amides, imidazolines,tetrahydropyrimidines, etc.

EXAMPLES The heterocyclic phosphonates of this invention, particularlythose of Examples 1 through 7, when tested exhibited corrosioninhibiting properties.

ACRlDlNE EXAMPLES AND CORROSlON TESTS EXAMPLE 8 Diethylacridine-9-phosphonate To a stirred suspension of acridine-N-oxide(19.5g; 0.1 mole) in diethyl phosphite ml) was added dimethyl sulfate(12.6g; 0.1 mole) dropwise at 1015 during 20 mins. The mixture wasstirred overnight at l5-20. To the resulting suspension was added asolution sodio diethyl phosphonate (from diethyl phosphite (50 ml) andsodium (2.3g)) during 20 min. at 10. After stirring 1 hr. at 10-l5 water(200 ml) was added and the mixture extracted with chloroform (3 X 50ml). Evaporation of the chloroform yielded a crude phosphonate which waspurified by chromatography on alumina and elution with chloroform. Finalpurification was performed by crystallization from benzene/hexanewhereupon diethyl a'cridine-9-phosphonate, mp 6, 16g (50%) was obtained.

Analysis calculated for n m iPz C. 64.76; H, Found: C, 64.64; H,

5.71; N, 4.44 P, 9.8471. 5.78; N, 4.20; P, 9.5671,

EXAMPLE 9 Acridine-9-phos-phonic acid 5]; H O, 12.2%. Found: N,

.8 P. 10.84; H O, 10.9%.

Corrosion tests were made using sand blasted 1020 mild steel couponsmonitored by a polarization resistance meter, a PAIR instrumentdescribed in U.S.P. 3,406,101. These tests were made in cylindricalcontainers of 1500 cc volume with provision for constant stirring bymeans of a motor driven impeller. A thermostatically controlledimmersion heater maintained an average temperature of 75C. and an airinlet kept the fluids constantly saturated with air. Between each testthe cylinder was cleaned with steam, benzene, acetone and thoroughlywashed with clean water. Results of these corrosion tests are shown inthe following Table.

Protection is calculated in the usual manner from corrosion rate (R,) offluids without inhibitor and corrosion rate (R in presence of particularinhibitor according to the formula (R, R /R X Percent protection.

TABLE Corrosion Results in Laboratory Brine (4.2% NaCl. 1.7% Mgcl 0.15%Cat'll 0.09% Nix- 504. PH 6.0)

In addition to the uses described above, these compositions and/orderivatives thereof can be used as follows:

l. as demulsifiers for O/W and W/O emulsions 2. as biocides i.e.bacteriocides, algicides, etc.

3. as additives to various petroleum fuels including gasoline, dieselfuel, jet fuels, etc.

4. as gasoline anti-icers and anti-stallers 5. as additives for sludgingoil and cutting oils 6. as agents for the textile industry such asmercerizing assistants, wetting agents, rewetting agents, penetratingagents, dispersing agents, softening agents, dyeing assistants, etc.

7. as anti-static agents for textile, plastics, etc.

8. as lube oil additives 9. as emulsifiers for insecticidal andagricultural compositions 10. as flocculants, particularly as flocaidsl 1. scale inhibitors 1 claim:

1. A process of inhibiting corrosion of ferrous metals caused by contactwith a corrosive medium which comprises contacting the metal with acorrosion inhibiting amount of a compound selected from the groupconsisting of diethyl acridine-9-phosphonate and acridine- 9-phosphonicacid.

2. The process ofclaim l where the compound is diethylacridine-9-phosphonate.

3. The process of claim 1 where the compound is acridine-Q-phosphonicacid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 88058 Dated April 29 1975 lnv-entorogy Derek Redmore It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Inthe title, "Phosphoric" should read Phosphonic In the Abstract, lines3 and 10, "phosphoric" should read phosphonic In the Abstract, lines 5and 7, "phoric should read phonic Bigncd and Scalcd this I i th D ay 0fDecember I 9 75 [SEAL] A ttest:

RUTH C. MASON Arresting Officer UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Patent No. 3,880,58 Dated April 29, 1975 wy Derek RedmoreIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In. the title, Phosphoric: should read Phosphonic phosphonic In theAbstract, lines 5 and 7, phoric" should read phonic Signed and Sealedthis BEAU ninth of December 1975 A ttes t:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner ojParenrsand Trademarks

1. A PROCESS OF INHIBITING CORROSION OF FERROUS METALS CAUSED BY CONTACTWITH A CORROSIVE MEDIUM WHICH COMPRISES CONTACTING THE METAL WITH ACORROSION INHIBITING AMOUNT OF A COMPOUND SELECTED FROM THE GROUPCONSISTING OF DIETHYL ACRIDINE9-PHOSPHONATE AND ACRIDINE-9-PHOSPHONICACID.
 2. The process of claim 1 where the compound is diethylacridine-9-phosphonate.
 3. The process of claim 1 where the compound isacridine-9-phosphonic acid.